Imaging devices are ubiquitous as camera phones and digital photography are available and relatively inexpensive. In late 2000, Sharp Corporation made the first consumer camera-phone (the J-SH04) marketed by J-Phone (Vodafone) in Japan. Studies report that in 2004, camera phone sales were four times higher than digital camera sales worldwide, and 60% of mobile phones sold in Japan had camera features. Moreover, the world-wide demand continues for improved image quality as well as lower cost in consumer devices capable of imaging.
One sort of imaging device, a charge-coupled device (CCD), is useful for recording and displaying images, and consists of an integrated circuit containing an array of linked or coupled capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to one or other of its neighbors.
CCDs containing grids of pixels are used in digital cameras, optical scanners and video cameras as light-sensing devices. Because CCDs commonly respond to 70% of the incident light (meaning a quantum efficiency of about 70%), CCDs are significantly more efficient than photographic film, which captures only about 2% of the incident light.
In CCD devices, an image is projected by a lens on the capacitor array, causing each capacitor to accumulate an electric charge proportional to the light intensity at that location. A one-dimensional array, used in line-scan cameras, captures a single slice of the image, while a two-dimensional array, used in video and still cameras, captures the whole image or a rectangular portion of it. Once the array has been exposed to the image, a control circuit causes each capacitor to transfer its contents to its neighbor. The last capacitor in the array dumps its charge into an amplifier that converts the charge into a voltage. By repeating this process, the control circuit converts the entire contents of the array to a varying voltage, which it samples, digitizes and stores in memory. Stored images can be transferred to a variety of output devices, including, for example, a printer, storage device or video display.
In consumer devices, there is a desire for the imaging device, whether such device be for image capture or image display or both, to be smaller, lower cost and “fool proof” (i.e., capable of producing a satisfactory image without any skill on the part of the operator). The expectation exists that images will increase in resolution. Current camera phones, for example, provide good resolution, with some models capable of as much as 7 megapixels (e.g., the Samsung SCH-V7700). Therefore, an imaging device capable of providing high resolution images is also desired.
Another expectation is the ability to take photographs or other images without having to explicitly set a focal depth.
Another expectation along with increased resolution is the recording of three dimensional (3D) position information.
What is needed is an imaging device that is inexpensive to manufacture and compact, with no moving parts and capable of focusing automatically. What is also desired is a single imaging device capable of recording position information in three dimensions.